On 9/22/2011 12:25 AM, Jeff Liebermann wrote:
On Tue, 20 Sep 2011 18:48:26 -0500, wrote:

I'm curious, I'm in a marina that has an L shaped concrete parking lot
with water on the inside of the L-- right were the arrow points.
I'm docked in the corner of the L, and want to send a signal everywhere
but the the water.

What does the pattern look like if I use a corner reflector but put
the source on the outside of the corner rather than the inside?

Dunno, and I'm too lazy (and tired) to build an NEC2 model. I don't
think it would work the way you propose anyway.

My guess(tm) is that you want to send RF in two directions, 90 degrees
apart. That's easy. Use 2 directional antennas, such as patch or
panel antennas, and drive them with a power splitter. You'll get half
the transmit power to each antenna, but the receive sensitivity will
be the same as it would be with a single antenna (minus about 1dB for
the power divider loss).

I'm at 433 Mhz now but may need to go to 2.4 Ghz.
The app is a driveway sensor that triggers a pocket carried receiver no
matter where I'm at on the L.

Ok. 433MHz has very limited range mostly because of the crappy
receivers, gutless transmitters, and miserable antennas. Improvements
to any of these will increase the range. I suggest a better antenna.

As it stands the transmitter range is not far enough, I only need 50
yards down leg of the L.

150 ft is difficult at 433Mhz. My cheapo La Crosse weather station is
only reliable up to about 20ft. My vehicle remote door unlocker is
good for only about 30ft. However, it is possible to buy long range
433MHz remote control switches, with much longer range. 2.4Ghz is
fine, but what are you going to use as a receiver?

I would need to purchase a pair, transmitter/receiver. Thinking about
it now, maybe I'll just get a walkie talkie set with a call button and
hack that to trigger from the driveway sensor. I did that with my PUSH
FOR SERVICE button years ago, worked fine until one of the walkie
talkies died.


Anyway, look at commercial wireless car alarms and notice that the
better variety have a small bi-directional remote, that can act as a
pager to receive alarms, and also be used as a transmitter to
enable/disable the alarm. These radios are probably better than
whatever you're using (and are probably on 900MHz). You might also
consider using a real pager and a POCSAG encoder.

At one time I hacked my cordless phone system so my PUSH FOR SERVICE
button closed the call button on the base unit and signaled the cordless
phone I carried in my pocket. I was never happy with the range of my
phone system though. The base is inside of my boat and the boat is a
double layer of aluminum, signal does get out, but I'm sure it is
attenuated.
I have had thoughts about removing the RF section of the phone and
putting outside, but there seems to be a lot of wires. Don't know how it
would work if I stuck 25 feet of ribbon cable between the phone and it's
RF section. Might be able to get that down to 15 feet.
Seems like I buy a phone system every 3 or 4 years the buttons start
getting flaky from living on the salt water. (the phone, not me)
So to state the problem;
I want to sense when a customer arrives and trigger an alarm I carry
in my pocket at a maximum distance of 150 feet.
If I can get the distance, I like the phone idea because I can also
answer phone calls.
I would attempt to run the RF signal outside, but I have not felt I
know enough about the impedance's to get a net gain after attaching
coax and an external antenna. Also I've noted 900Mhz transmit and 5.1
Mhz receive, or some such scheme. That makes the antenna difficult.

Just thinking in public :-)
Mikek